The inventors of this invention have introduced S-FOLM (Scalable Film Optical Link Multi-chip-module) and its resource-saving process PL-Pack with SORT (Photolithographic Packaging with Selectively Occupied Repeated Transfer) as a low-cost and resource-saving technology for high-density integration of thin-film electronic devices and thin-film optical devices (optoelectronic system integration technology) (T. Yoshimura, J. Roman, Y. Takahashi, M. Lee, B. Chou, S. Beilin, W. Wang, and M. Inao, Proc. SPIE 3952, p. 202 (2000)).
S-FOLM is explained hereinafter, taking an optical module for optical communication as an example. In integration processes prior to the introduction of S-FOLM, bulk chips of optical devices and electronic devices have been mounted on a printed circuit board by flip-chip bonding. In S-FOLM, on the other hand, thin-film devices created on a wafer are transferred and embedded in a waveguide printed circuit board by a process such as Epitaxial Liftoff (ELO). Then, an interface film with embedded thin-film IC is deposited thereon. Such a stack architecture enables space saving. It also allows a shorter metal line length, reducing noise. Further, it achieves cost reduction with a scalability specific to a film lamination architecture. With S-FOLM, various optoelectronic systems may be implemented including a smart pixel, OE (Optoelectronic)-LSI, OE-MCM (Multi Chip Module), OE-PCB (Printed Circuit Board), and 3D system LSI.
PL-Pack with SORT has been introduced as an embedding process of thin-film devices necessary for producing S-FOLM. The process disposes thin-film devices on a substrate, embeds the thin-film devices in a polymer film, and then forms electrodes, pads, and via holes. SORT is a technique that improves the efficiency of a critical step of the thin-film device transfer and disposition process. In the integration of VCSEL (Vertical Cavity Surface Emitting Laser), for example, the first VCSEL array is created on a wafer, and, after tested, it is transferred to the first supporting substrate in a specific arrangement by the ELO process. Similarly, the second VCSEL array is transferred to the second supporting substrate. Then, a substrate with capture pads made of metal or polyimide is prepared, and the first and second supporting substrates are sequentially brought into contact thereto. The two kinds of VCSEL are thereby disposed on the substrate in a desired layout. The remaining VCSEL left on the first and second supporting substrates are disposed in a different place or a different substrate. The process thereby saves resources. For cost reduction, it saves expensive semiconductor epitaxial material, using the epitaxial material only in a site where it is necessary while using polymer in the other area. Further, with one-time processing by a semiconductor photolithography process, alignment accuracy is improved and process reduction is achieved. Furthermore, conventional mounting processes can be eliminated, permitting easy integration of different kinds of devices.
S-FOLM, however, provides no architecture of an optical switching system that is expected to form the core of the next generation optical technology. For high-speed, high-capacity communication network, a large scale optical switching system is required. A prototype of MS system for optical crossconnect with a scale as large as 1000×1000 channels has been developed using MSMS (Micro Electro Mechanical Systems). High-speed optical switching as fast as microseconds to nanoseconds, however, requires waveguide devices such as electro-optical switches and semiconductor gate switches. Creating a large-scale version of such a system has various difficulties including complex waveguide lines and a large optical circuit size. In the absence of a promising system architecture, there is a need for architectural breakthroughs.
Further, SORT has a problem that a thin-film transfer process is complicated, causing cost overrun of an entire system. It also has a problem that the thin-film transfer process requires creation of a multiple adhesive hierarchy of thin-film devices and a substrate. Thus, there is restriction that the device transfer in later stages needs higher adhesive strength. This not only narrows down the choices of materials, but also reduces process margins, destabilizing the process. Furthermore, elimination of pads is needed since they can be obstacles in system design.
Besides, S-FOLM and other technologies have provided no detail of the bonding interface of a drive IC and an optical device, particularly those with multiple fine electrodes such as Variable Well Optical IC (VWOIC) (Japanese Unexamined Patent Application Publication No. H4-181231 and H4-204633, T. Yoshimura, FUJITSU Sc. Tech. J. 27, p 115 (1991)).
An object of the present invention is to provide a high-speed optical switching system as large as 1000×1000 channels and as fast as microseconds to nanoseconds, for example, with a new architecture based on 3D micro optoelectronic system (3D-MOS).
Another object of the invention is to provide a low-cost and reliable thin-film device transfer process (which may be called “Light Assist SORT (LA-SORT)”) using control of the adhesive strength of an adhesive bond by multiple stage exposure.
A further object of the invention is to provide an improved architecture of an interface between an optical switch and a drive IC, to provide a basic architecture of an all-optical 3D optoelectronic microsystem, and to provide a new architecture of a micro filter of a 3D optoelectronic microsystem.
A still further object of the invention is to provide a transfer and disposition process of micro devices called “Adhesive Hierarchy Assist SORT (AHA-SORT)” which uses a series of adhesive bonds with adhesive hierarchy, allows reuse of the adhesive bonds, and is realizable with a simple process.
Another object of the invention is to provide a system film, a system thread, a system cloth, an artificial retina, an artificial skin, a solar cell, and a display using the above.